Transportation fuels, such as gasolines, diesel fuels, and jet fuels, as well as light heating oils, are high-volume, high value refinery products. While light heating oils are not transportation fuels, their hydrocarbon components are usually interchangeable with diesel and jet fuels, differing primarily in their additives. Thus, it is a major objective of petroleum refineries to convert as much of a barrel of crude oil into transportation fuels as is economically practical. The quality of crude oils is expected to slowly worsen with increasing levels of sulfur and metals content and higher densities. Higher densities mean that more of the crude oil will boil above about 560° C., and thus will contain higher levels of Conradson Carbon and/or metal components. Historically, this high-boiling material, or residual, has been used as heavy fuel oil, but the demand for these heavy fuel oils has been decreasing because of stricter environmental regulations. This places a greater demand on refineries to convert as much of a barrel of crude as possible to more valuable lower boiling products.
In a typical refinery, crude oils are subjected to atmospheric distillation to separate lighter materials such as straight run naphtha, gasolines, kerosenes, gas oils, etc. from the heavier materials. The residue from atmospheric distillation is then distilled at a pressure below atmospheric pressure. This latter distillation step produces a vacuum gas oil distillate and a vacuum reduced residuall oil that often contains relatively high levels of asphaltene molecules. These asphaltene molecules usually contain most of the coke forming and metal components of the resid. They also contain relatively high levels of heteroatoms, such as sulfur and nitrogen. Such residual feeds have lower commercial value, primarily because they cannot be used as transportation fuel or as heating oil because of ever stricter environmental regulations. They also have lower value as feedstocks for refinery processes, such as fluid catalytic cracking, because they produce excessive amounts of gas and coke. In addition, their high metals and heteroatom content leads to catalyst deactivation. Thus, there is a need in petroleum refining to upgrade residuall feeds to more valuable cleaner and lighter products.
There are a number of processes used for recovering the lighter components from various asphaltic petroleum residual feeds. Some of these processes involve the extraction of the lighter components with a deasphalting solvent, and thereafter separating and recovering the lighter components from the solvent. The solvent utilized is a liquefied, but normally gaseous, solvent, such as propane, which is maintained at a temperature between about 38° C. (100° F.) and 121° C. (250° F.) and at a pressure sufficient to maintain the solvent in a liquid phase. While propane is often used in conventional solvent deasphalting operations, other solvents such as butane, pentane, hexane, and mixtures thereof have also been suggested.
Typically, solvent deasphalting is followed by processing the deasphalted oil in a hydrotreater and catalytic cracker, while the asphaltenes are processed in a delayed or fluid coker. While such processes have met with commercial success, there is nevertheless a continuing need in the art for an enhanced deasphalting process, which results in higher liquid yields and an increased capacity for processing residual.